Why does PP filament warp 2 hours after the print starts

I’m printing with Basf Ultrafuse PP GF30 filament and I’m having issues with it warping. The problem is I get a perfect first layer and everything sticks fine. I come back an hour later and everything is still going perfectly but a little after two hours it starts to warp. I want to say its not a first layer issue but im not completely sure. As a test I’ve been printing a 3"x4"x.25" square with rounded corners. My settings for the best prints so far is a 247c nozzle temp, 28c bed temp with pp tape, 40mm/s speed, 91% flow, 50% fan speed, and .15mm layer heights. I’m using a .4mm nozzle and have calibrated the z offset to make pretty nice first layers. I have tested bed temps of 28c, 30c, 35c, 40c, 70c, 85c, and 90c. I have tested nozzle temperatures from 230c-280c in increments of 5. I did a flow cube calibration test which is where I got the 91% flow from. Finally I have tested fan speeds of 0%, 25% and 50%. I know PP filament is pretty hard to print but is it impossible to have no warping. Should I boost the fan speed way, slow down the print speed, increase layer height? I’m kind of running out of ideas to test now.